Maintenance, Repair, and Troubleshooting
What this domain tests
This domain tests diagnosis before repair. Expect questions on slow or blocked drains, leaks, low pressure, running toilets, water-hammer noise, frozen pipes, water-heater problems, and backflow testing. The best answer usually identifies the cause with a test rather than replacing parts at random.
Core troubleshooting rules
- A single slow drain points to a local clog or vent issue; multiple slow fixtures suggest a main-line or vent problem. Snake or jet the line, then camera it if the blockage recurs.
- Gurgling after draining usually means a blocked or inadequate vent. Check the trap, the vent, and any AAV before assuming the drain is clear.
- Low pressure at one fixture: check the aerator, supply stop, and flexible connector. Low pressure everywhere: check the PRV, meter, and galvanized scale.
- A running toilet is usually a flapper, fill valve, or overflow-height problem. Replace the flapper first if it is warped or dirty.
- Water hammer after a valve closes suggests a failed arrestor, loose pipe, or excessive pressure. Secure the pipe and check the PRV.
- Frozen pipe: shut off water, open a faucet, and thaw with warm air or a heat gun-never an open flame. Water heaters need sediment flushing and anode-rod checks.
Worked example
A second-floor shower drains slowly and gurgles, but the lavatory drains normally. The local shower trap or trap arm is the likely restriction, and the gurgle suggests the vent is partly blocked. Snake the trap arm, check the vent, and test the shower before replacing the trap. If the gurgle persists, inspect the vent terminal.
Traps that cost marks
Pouring chemical cleaner into a line that needs mechanical cleaning, overtightening plastic trap parts, and replacing a fixture without confirming the supply or drain is actually the problem.
Key points
- One slow fixture suggests a local clog; several suggest a main or vent problem.
- Gurgling points to venting, not just drainage.
- Check aerators and stops first for single-fixture low pressure.
- Never thaw frozen pipe with an open flame.
- Diagnose with a test before replacing parts.